The disclosure of Japanese Patent Application No.2002-308630 filed on Oct. 23, 2002 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an estimation apparatus of an air intake flow for an internal combustion engine.
2. Description of Related Art
An appropriate control of a combustion air/fuel ratio requires accurate estimation of an air intake flow fed into the cylinder. Generally an air flow meter disposed upstream of a throttle valve has been used to detect the air intake flow, or a pressure sensor disposed downstream of the throttle valve has been used such that the air intake flow is derived from the detected pressure of an intake pipe. Each of the aforementioned sensors, however, fails to provide the accurate air intake flow independently. Accordingly, there has been proposed to combine different kinds of the aforementioned sensors so as to obtain the accurate air intake flow.
For example, a change xcex94Gin in the air intake flow rate fed into the intake pipe is calculated based on a variance in the pressure of the intake pipe downstream of the throttle valve, which is detected by the pressure sensor. Then the calculated change xcex94Gin is added to an air intake flow rate Gafm detected by the air flow meter to obtain an air intake flow rate Ge currently fed into the cylinder. Considering the response delays of both the air flow meter and the pressure sensor, there has been proposed for correcting the air intake flow rate Gafm and the change xcex94Gin to values in order to compensate such delays using the respective time constants (see Related Art No. 1). Other documents as related art of the invention will be listed below:
Related Art No. 1: JP-A-2002-70633 (paragraphs [0022] to [0032]);
Related Art No. 2: JP-A-7-189786;
Related Art No. 3: JP-A-10-227245;
Related Art No. 4: JP-A-10-274079;
Related Art No. 5: JP-A-4-12148; and
Related Art No. 6: JP-A-2-108834.
The actual air intake flow fed into the cylinder is defined by the air intake flow rate at an intake valve closing timing. The timing for calculating the air intake flow rate, however, is required to be at least prior to the timing for starting the fuel injection, i.e., far before the intake valve closing timing. In a normal state of the internal combustion engine, the calculated air intake flow rate is substantially in accord with the actual air intake flow rate at the intake valve closing timing. Accordingly, the estimated air intake flow is relatively accurate. Meanwhile in a transient state of the internal combustion engine, there may be a clear difference between the calculated air intake flow rate and the actual air intake flow rate at the intake valve closing timing. In this case, the actual air intake flow cannot be estimated accurately.
It is an object of the invention to provide an estimation apparatus of an air intake flow for an internal combustion engine, which is capable of accurately estimating the air intake flow fed into the cylinder.
An estimation apparatus of an air intake flow for an internal combustion engine includes a pressure sensor that detects an intake pressure in a portion just upstream of an intake valve of an intake system of the internal combustion engine and an air flow meter that detects an air intake flow rate fed from an upstream side of the intake system to the portion just upstream of the intake valve. In the estimation apparatus, a first air intake flow rate fed into the portion just upstream of the intake valve at a predetermined timing prior to a timing for starting fuel injection is obtained based on an output of the air flow meter, a variance in an air intake flow rate caused by a change in the intake pressure in the portion just upstream of the intake valve is obtained based on an output of the pressure sensor, a second air intake flow rate fed into a cylinder of the internal combustion engine at the predetermined timing is obtained by adding the first air intake flow rate to the variance in the air intake flow rate. Then the second air intake flow rate fed into the cylinder is corrected to a third air intake flow rate required for estimating an actual air intake flow based on an amount of change in the second air intake flow rate fed into the cylinder at the predetermined timing.
An estimation apparatus of an air intake flow for an internal combustion engine includes a pressure sensor that detects an intake pressure in a portion just upstream of an intake valve of an intake system of the internal combustion engine and an air flow meter that detects an air intake flow rate fed from an upstream side of the intake system to the portion just upstream of the intake valve. In the estimation apparatus, a first air intake flow rate fed into the portion just upstream of the intake valve at a predetermined timing prior to a timing for starting fuel injection is obtained based on an output of the air flow meter, a variance in an air intake flow rate caused by a change in the intake pressure in the portion just upstream of the intake valve is obtained based on an output of the pressure sensor, a second air intake flow rate fed into a cylinder of the internal combustion engine at the predetermined timing is obtained by adding the first air intake flow rate to the variance in the air intake flow rate. Then the second air intake flow rate fed into the cylinder is corrected to a third air intake flow rate required for estimating an actual air intake flow based on an amount of change in a state of a mechanism of the internal combustion engine at the predetermined timing, the mechanism giving an influence on the air intake flow.
In the estimation apparatus, a state of the mechanism that gives an influence on an actual air intake flow is estimated based on an amount of change in a state of the mechanism at the predetermined timing, a difference between an air intake flow rate estimated based on the estimated state of the mechanism and an intake air flow rate fed into the cylinder at the predetermined timing that is estimated based on the estimated state of the mechanism at the predetermined timing is calculated. The calculated difference is added to the second air intake flow rate so as to be corrected to a third air intake flow rate required for estimating the actual air intake flow such that an air intake flow fed into the cylinder is estimated.